Poly(vinyl chloride), polymerized with the use of γ‐radiation, benzoyl peroxide, and 2,2′‐azobis(isobutyroitrile) as initiators, was thermally decomposed in vacuo. The gaseous decomposition products as analyzed by mass spectrometry consist primarily of hydrogen chloride for decomposition temperatures below approximately 300°C. At temperatures approximating 400°C., various hYdrocarbons are evolved along with the hydrogen chloride. Energetic considerations are discussed and the activition energy is determined. A free radical mechanism for the dehydrochlorination reaction that appears consistent with the reaction rate data for a three‐halves‐order reaction is postulated.

Films of polyamides were exposed to heat, ultraviolet radiant energy, and different atmospheric conditions. The degradation products were collected in some cases and analyzed by mass spectrometric techniques. The unexposed and exposed specimens were examined by the following techniques to obtain information concerning the changes in chemical and physical structure of the polymer: infrared absorption, ultraviolet absorption , viscosity of solutions, measurement of dielectric constant and dissipation factor, photomicrography, X-ray diffraction, electron microscopy, electron diffraction, and effect of organic liquids. In addition, pyrolysis studies were made and some physical properties were determined. The results of the investigation show clearly that no single method gives a complete picture but that the results from several of the methods give an insight into the mechanism of degradation of poly ami des.Polyamide molecules are relatively unaffected by exposure to moderate temperature (60 0 C). However, loss of water and other volatile materials may cause changes in physcial properties. The effects of exposure to ultraviolet radiant energy are more pronounced, and degradation of the polyamide molecule occurs with accompanying loss of water and other volatile materials that act as plasticizers.The results of this inves tigation show that the general course of the degradation of polyamides is as follows :1. The polymer mol ecules break at the C -N bond of the peptide group creating smaller polymer molecules with the same unit of chemical structure. The fragments broken out are evolved as carbon dioxide, carbon monoxide, water, and hydrocarbons.2. The degree of crystallinity or local order changes, including alterations in hydrocarbon packing, dipole rearrangement, and hydrogen bridging.3. The amount of strongly bound water and/or organic liquids changes. These materials are probably bound by hydrogen bridging to the oxygen of the peptide group. They act as plasticizers for the polyamides. r. IntroductionOne of the major problems facing the plastics industry is the degradation of some plastics when exposed to certain service conditions. This problem has been investigated extensively by accelerated tests involving one or more physical properties. While empirical investigations of this type give information of value, they yield little or no information on the basic changes in the material. As a result, the value of the information now aVi),ilable is not only limited, but in too many instances the information cannot be used to predict behavior in actual service [1).1 The physical changes observed during degradation may result from (1) changes in the chemical structure of the plastic material, and (2) loss or changes in the compounding ingredients. The logical method of attack is to determine the specific chemical reactions involved in the degradation of the plastic and how these reactions are affected by the intensity of the conditions encountered.The degradation of the plastic type of polyamides was investigated as p...

The cha nges in chemical structure occu ring in pol y (vinyl chloride) as a res ul t of heati ng ina vacu um in t he range 100° to 400° C wer e studied using infrared spectropho to metry. The pri ncip a l changes occ urri ng in t he residue during p yrolysis in a vacuum were the format ion of unsaturated s tructures a nd a change from a n al iphatic spectrum to one showing aroma tic absorption. The data are used to suppor t a previou sly proposed mechani sm of decomposition for poly (vinyl chloride) .

Twelve plastics representing various chemical structures were studied as part of a program to determine the utility of plastics as packaging materials in the high radiation presentation of food. The plastics were exposed to selected dosages of Cobalt‐60 gamma radiation in vacuum and in air. Gas evolution and changes in infrared spectra as a result of irradiation were used to hypothesize the relative stability of these plastics to irradiation. Based on these facts it was found that plastics containing conjugated ring systems, ionic linkages, and chlorine in side groups were the most stable.

Sin ce p olystyrene is a widely used plastic a nd styrene is an in tegral part of t he m ost wid ely used sy nthetic r ubber (GR-S) , it appears necessary to k now somethi ng of the process of degrada t ion of polystyrene t o a ssist in in terpreting t he d egradation of these materi als in service. P olystyrene films were exposed to h eat at 100° C in a for ced-draft air oven a nd to ultraviolet ra di a nt e nergy at 60° C in air. Chemical st r uctural changes in t he polymer a s a resul t of t hese t reatments were a nalyzed b y st udy of t he infrared spectra between 2 a nd 16 microns , obtained wit h a Ba ird recording infra red spectrop ho tomete r. U lt rav iolet expos ure fo], 200 hours resulted in a bsorpt ions a t 2.9 and 5.8 microns, which a re attributed to hydroxyl a nd carbonyl groups, respectively. H eati ng of t he film for 270 hours at 100° C p rodu ced no signifi can t change in the infra red spectrum. P ro longed heating at. 125° C resul te d in t he dest r uction of t he films by £i ow. The literature and t heory o n t he d egrada t io n of p olys tyrene a re discussed. Several me cha nis ms are postu lated to a ccou nt for the p rod uction of hydroxyl a nd carbonyl p rodu cts in t he p oly mer .